6 answers
Hi Kim,
In that case I would use DataLoader.io. First run an export of the data in question by filtering on the field that will allow you to isolate the records. The export serves three purposes (1) you can verify that you are targeting the correct data (2) you have a back-up of what you are about to delete (3) To delete records you need to have a list of IDs you wish to delete.
Then you can run your delete job using the export file you just created. See the following step by step guide for deleting records using DataLoader.io
Deleting records (https://dataloader.io/deleting-data-salesforce)
You can use the Salesforce DataLoader or another thrid party data loader such as JitterBit and the steps will be very similar. DataLoader.io is generally recognised as the best of the free dataloader tools available.
Let us know if you have any further questions.
Thanks
Damien